Equations have been derived which apply with and allow quantitation of cation transport damage which is an almost invariable concomitant of cataract. The equations require lens and media electrolyte data and assume conditions of flux equilibrium and the validity of the Ussing flux ration equations. With total lens cation transport failure, lens protein dialysates conform to a Donnan equilibrium situation. Thus, it is theoretically possible to classify cataracts biochemically based on their hydration and degree of cation transport damage as measured by electrolyte changes. Preliminary investigations demonstrate that human senile and certain experimental cataract data conform to theoretical expectations. We intend to produce cataracts in albino rabbits by intravitreal injection of cetylpyridinium chloride (CPC), classify the cataracts clinically, then determine lens Na ion, K ion and % H2O. With this information we can classify the lenses according to the degree of cation transport failure and attempt to correlate this with severity of clinical damage. Similar clinical and biochemical studies will be continued on human senile cataracts. In addition, the physical properties of lens protein dialysates will be explored.